1. Field of the Invention
The present invention relates to a resist material and, more particularly, to a novel chemically amplified resist material which can exhibit a high resolution, high sensitivity, excellent resistance to dry etching and can be produced at a low cost. The present invention also relates to a process for the formation of resist patterns using such a novel resist material. The resist material of the present invention can be advantageously utilized in the production of semiconductor devices such as semiconductor integrated circuits, for example LSIs, VLSIs and ULSIs, and other devices.
2. Description of the Related Art
Recently, in the production of semiconductor integrated circuits, the degree of integration thereof has notably increased and, accordingly, LSIs and VLSIs have been produced on a commercial scale. The minimum line width of the circuit patterns in these devices approaches the order of a submicron or a quarter micron. In other words, in the production of these high performance devices, it is required to provide a fine fabrication technology for forming fine resist patterns.
Using a fine fabrication technology, fine resist patterns can generally be produced by coating a substrate having on a surface thereof a layer or coating to be fabricated, such as a layer to be selectively etched, with a chemically amplified resist material, and exposing the resist film to patterning radiation to thereby form a latent image corresponding to a pattern of said radiation. The latent image of the resist film is then developed with a suitable developer. A desired resist pattern is thus obtained. The resist pattern can be effectively utilized as a masking means in the subsequent dry etching process to selectively etch the underlying layer. The patterning radiation generally includes ultraviolet radiation such as the g-line (wavelength of 436 nm) and i-line (wavelength of 365 nm). However, it also includes other radiation having shorter wavelengths such as deep ultraviolet radiation, vacuum ultraviolet radiation, electron beam (EB), X-ray and others as well as excimer laser radiation such as KrF laser radiation of the wavelength of 248 nm and ArF laser radiation of the wavelength of 193 nm. Note that the term "radiation" used herein means all of the above-mentioned radiations.
In the formation of submicron-ordered resist patterns using as patterning radiation in the far ultraviolet or vacuum ultraviolet regions, it is necessary to use specific resist materials having an excellent transparency to the patterning radiation and also a high resistance to dry etching. The inventors of this application have studied this and found that said need is satisfied by a radiation-sensitive material comprising a polymer or copolymer of acrylic acid ester or a-substituted acrylic acid ester in which the ester portion contains an adamantyl skeleton (see, Japanese Unexamined Patent Publication (Kokai) No. 4-39665).
Further, in Japanese Unexamined Patent Publication (Kokai) No. 9-73173, the inventors of this application have suggested a chemically amplified resist material which comprises an acid-sensitive, alkali-insoluble compound and a photoacid generator capable of producing an acid upon exposure of the resist material to a patterning radiation. The acid-sensitive, alkali-insoluble compound is characterized by containing a protected alkali-soluble group in which an alicyclic hydrocarbon group having, bonded to a carbon atom thereof, a lower alkyl group is contained as a protective group, and it is cleaved from the alkali-soluble group upon action of an acid so that the compound becomes alkali-soluble. Using this resist material in the formation of fine resist patterns, since the alicyclic hydrocarbon group can be cleaved and thus removed from the resist material, it becomes possible to inhibit peeling off of the resist patterns from the substrate during the development process.
In addition, in Japanese Unexamined Patent Publication (Kokai) No. 9-90637, the inventors of this application have suggested another chemically amplified resist material which is characterized by using, in combination, an acid-sensitive polymer with the monomeric unit having in a side chain thereof a protective group-containing carboxyl group, the protective group being a specific lactone structure, and a photoacid generator. Using this resist material, it becomes possible to form fine resist patterns having a practically usable sensitivity and an excellent adhesion to the substrate, because of presence of the specific lactone structure.
As is described in detail in each of the above-referred patent publications, the chemically amplified resist materials invented by the inventors of this application can provide many attractive effects. In particular, the resist materials having both of a cleavable cyclic hydrocarbon structure and a lactone structure can exhibit highly improved performances. These resist materials, however, suffer from a high production cost. This is because, in the production of the resist materials, particularly in the production of a monomer with the lactone structure used as a starting material, various steps of the production are required, and a purification of the monomer must be carried out using a purification column, because the conventional distillation process cannot be used. Further, the lactone structure, since it contains oxygen atoms in a high content, can deteriorate a resistance to dry etching.